A comparative study on microstructure and mechanical properties between friction and laser beam welded titanium tubes

摘要

The microstructure and mechanical properties of friction and laser beam welded Grade 2 titanium tubes (wall thickness of 3.9 mm and outer diameter of 60 mm) are compared in the present investigation. Friction welding (FW) was conducted on a vertical friction processing system. Laser beam welding (LBW) was accomplished by utilizing a 4 KW Nd:YAGlaser. The microstructure evolution was observed by optical microscopy and advanced techniques such as TEM and EBSD. The friction welded joints showed fine grains due to dynamic recrystallization. A variation in grain size towards the outer circumference of the tube was observed due to flash formation. The laser beam welded joints displayed large grains with irregular boundaries. Both joints exhibited an elevated dislocation density due to severe plastic deformation and thermal stresses respectively. Strengthening of the joint area was recorded in both joints albeit due to different strengthening mechanisms. The failure location, during mechanical testing, occurred in the base metal for both processes. Overall when compared, LBW is probably the preferred process to join these tubes due to its higher welding speed and therefore reduced production cycle.